The field of this invention is that of electrical heaters and the invention relates more particularly to self-regulating heaters having electrical resistance heater elements of a ceramic material of positive temperature coefficient of resistivity and to early fuel evaporation systems for automotive engines using such heaters.
Early fuel evporation (EFE) systems for automotive engines have electrical heaters heating the air-fuel mixture which passes to the engine during the engine warm-up period to enhance fuel evaporation on a cold day, thereby to assure smooth engine starting or to reduce exhaust pollution emissions. Some heaters comprise thin electrical resistance heater discs of a ceramic material of positive temperature coefficient of resistivity which is adapted to display a sharp increase in resistance when the heater self-heats above a particular transition temperature such as 80.degree.-180.degree. C. Those heater discs are self-regulating in that they display progressively increasing electrical resistance and reduced heat output as the heater temperature increases until the heater temperature stabilizes at a safe level.
In certain well known EFE systems presently in commercial use, the heater includes a metal radiator body of substantial size and thermal conductivity having one heat-transferring side provided with heat-distributing rods or fins. Usually, one flat side of each of the thin ceramic heater discs is secured in electrically and thermally conducting relation to an opposite heat-receiving side of the radiator and the radiator is connected to electrical ground. Electrical terminal means engage the respective opposite sides of the heater discs for electrically connecting the resistance heater discs in parallel relation to each other. In that arrangement, the heater discs are conveniently energized from the battery or generator power source of the automotive engine when the engine is started by closing of the ignition switch and are adapted to effect efficient transfer of heat to the radiator for rapidly heating the air-fuel mixture during cold weather to achieve smooth engine performance during start up while reducing emission of pollutants from the engine exhaust.
However, it is found that, as the radiator body of the heater is subjected to thermal expansion and contraction during repeated heating and cooling of the EFE system, the electrical and thermal bond between the heater discs and the heat-receiving side of the radiator body can be broken resulting in breaking of the heater-energizing circuit. It would be desirable if an economical and efficient means could be provided for electrically and thermally connecting the resistance heater discs to the radiator body and for assuring that such electrical and thermal mounting of the heater discs would be reliably maintained throughout a long service life.
It is an object of this invention to provide a novel and improved self-regulating heater device; to provide such a heater device which is particularly adapted for use in an early fuel evaporation system for an automotive engine; to provide such a heater device which is adapted to furnish a desired heating effect with high heating efficiency; to provide such a heater device having improved reliability for use in an automotive environment; and to provide a novel and improved fuel supply system for an automotive engine utilizing such a heater device.